Vacuum tube grid construction



Feb. 1, 1949. H. SELVIDGE.

VACUUM TUBE GRID CONSTRUCTION Filed Jan. 15., 1945 ATTORNEY HARNEA EET M Patented Feb. 1 1949 VACUUM TUBE GRID CONSTRUCTION Harner Selvidge, Silver Spring, Md, assignor to the United States of America as represented by the Secretary of the Navy Application January 15, 1945, Serial No. 572,940

2 Claims. (01. 250-215) The present invention relates generally to electron tube construction and more specifically to.

an improved control electrode structure suitable for incorporation in tubes of all types, particularly grid-controlled gas-filled tubes. Prior-art vapor-electric discharge devices ar generally so constructed that when the individual tube becomes conductive the are between anode and cathode touches the cathode at some random point determined by the potential distribution, with the result that the impedance of that portion of the cathode between the'point thereof touched by the arc and one end thereof is included in the work or outputcircuit. The flow of anode current through this added impedance may consume a considerable portion of the output energy of the tube so that when the tube is employed in a detonator firing circuit the efficiency ofrfiring may be impaired by reason of the diminution of energy available at the detonator igniter terminals.

The'primary object of the present invention is, therefore, to increaseoutput energy by providing a new and improved control electrode structure that restricts current fiow'to that part of the cathode that is electrically proximate to the output circuit so that the impedance of a major portion thereof will not be imposed on the output circuit. This consideration is of particular importance in tubes having the filamentary type of cathode because of the high resistance of the filament.

Another object of the invention is to provide such a structure that is relatively simple in arrangement and highly eflicient in operation.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings, in which Fig. 1 is an elevational sectional view of a gasfilled, grid-controlled, filament-type tube constructed in accordance with the present invention, suitably connected circuit components being diagrammatically illustrated;

Fig. 2 is a detail perspective fragmentary view illustrating the operation of the invention;

Fig. 3 is a detail-perspective, fragmentary view of a modified form of grid construction suitable for incorporation in the tube represented in Fig. l; and

Fig. 4 is a view similar to Fig. 1 showing the invention in somewhat modified form as applied to a tube of the indirectly heated cathode type.

With reference now specifically to Fig. 1 there contact prongs l2, 13, Hi, and I6. The prongs are individually electrically connected, respectively, to an anode 20, to one terminal of afilament 22,-

4 to the other terminalof the filament,.andsto. a. The filament 22 is supplied The input: con-e;

control electrode .24. with current from a battery l8. tacts I4, iii are coupled to input terminals 26,121

of a control circuit in a conventional manner.

The output terminals 12, M are connected to a work circuit comprising an anode battery 28 and a firing heater 29 of an electrically operable. primer (the other components of which. are:'not shown), also in a manner well known to those: A suitable source 18 i of: fila-v skilled in the art. ment current is coupled to the contacts 131 .14.

Concentric with the longitudinally disposed filament 22 is a generally tubular metallic control;

electrode or grid 24. Disposed between-'theigrid 2d and the envelope is a generallytubular metal-.

anode 20. The general arrangement of these parts may be conventional in character, as shown. An important feature of the invention, however,

resides in the provision in the otherwise continuous grid 24 of one or more slots 3B, 3! at the extreme ends of this electrode, whereby the grid becomes a beam-confining electrode for restricting anode current flow to that part of the filament electrically proximate to the output circuit,

thereby effectively minimizing the impedance of the anode-filament current path, in a manner specifically to be explained in the following description of the operation of the electron tube.

In the filamentary type of tube, the filament is not at a uniform potential throughout its length with respect to the grid or anode because of the voltage drop in the filament caused by the flow of heating current therein. When a positive triggering potential is placed on the control electrode, one end of the filament is more negative with respect to the anode than the other end, depending upon the connections of the filament battery H3. The major flow of anode current would tend to occur at this more negative end because of the potential distribution, if the grid slot were to run the full length of the grid. The disposition of the grid slots only at each end of the filament, however, insures that the arc will strike one of the other end of the filament. In the embodiment illustrated electron flow will occur through the slot 3 I since it is located adjacent to that part of the filament that is electrically proxis is illustrated therein a tube of the gas-filled gride controlled type, indicated generally at H], having." a glass envelope l l and an integral basecarrying mate to the negative terminal of the battery l8.

Thisoperation is illustrated in detail in Fig. 2.

If the battery terminals were reversed, electron flow would occur through the slot 30. In that case, the contact' I3 should be coupled to the grounded side of the work circuit.

1 The Fig. 4 embodiment differs from that illustrated in Fig. 1 ink that an'indirectly heated cathode 23 and heater are substituted for the filament,

and in the provision of only a single slot, 3], in

the grid at the grounded end of the cathode. The contacts and circuit connections are modifiedac-r cordingly in a conventional manner.

In the indirectly heated type of gas tube, the

cathode is. at substantially uniform potential along its length. If the grid slot were coextensive with the grid, the arc. would'touch-the cathode at some random point.

Sincethe grid slot 3|, however, is placed near the end of the cathode to which the external cathode lead is coupled-at the contact I5, anodecurrentflows beinvention and it is, therefore, intended in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. An electronic tube comprising an envelope,

an anode disposed longitudinally within the said anode,a filament extending longitudinally within tween the portion of the cathode near that end I and the anode,- so that-'a-minimum of resistance is imposed on the output circuit of the tube. This portion-of the cathode is electrically proximate to the output circuit. The nature of the anodenection: with the embodiment first described is p of course similar in the embodiment of Fig. 4.

In Fig. 3a modified form ofgrid construction is shown. In order to prevent deformation of the grid slot when the tube is subjected to rough handling, a. reinforcing strap 34 bridging the lower margins of the-grid adjacent-the slot is provided. This strap, shown welded in place,. might of coursebe punched as an integral part of the grid.

-While there havebeen described what are at presentconsidered to be preferred embodiments of this invention,it will be obvious to those skilled in'theiart that various changes and modifications maybe madetherein without departing. from the 7 cathodecurrent path illustrated in Fig. 2 in 0011- the said anode and in spaced relation thereto, and a control electrode between the filament and the anode, said control electrode having an opening at each end an'dbeing: 0t approximately zthe same longitudinal extent as the said fil'amentpth'e said control electrode thus shielding the filament from the anode except adjacent the endsaof 'thesaid filament, and thereby forcing-the electrical discharge within the gas to occur at onnearan end of said filament. I

' HARNERaSELVIDGE.

REFERENCES CITED;

The following references are of record in the filefof. this patent:

UNITED STATES:- PATENEIS- Number 1 la1ne Date 2,039,449 Radcliff etel. May5, 1936 2,044,618- Livingston; June-16, 1936 2,051,081 Fritz Aug: 18, 1936 2,054,234 Allen Sept. 15, 1936 2,080,235 Smith May 11, 1937 2,139,593 Putzer Feb; 6, 1940 2,212,849 Slack'et' al; Aug. 27, 1940 

